6 Wood Discoloration

8.5 Damage to Structural Timber Indoors 219
forms placenta with salmon-pink fruit bodies (“Reddish sap polypore”) and
monticola, never with reddish stain (Domański 1972). Monokaryotic isolates
of O. placenta were used for testing wood preservatives in Germany (Poria
vaporaria “standard strain II”) and are obligatory in the recent European
standard EN 113 (see Table 3.9, 3.10, named “Poria placenta” FPRL 280). Even
literature from 2005 uses the names Postia placenta and Poria placenta.
For species identification in the case that only vegetative mycelium is present,
rDNA-ITS sequencing separates the five species (Schmidt and Moreth 2003;
Chap. 2.4.2.2).
For an easier understanding during a practical valuation of a fungal damage,
the different fungi are often summarized as “indoor polypores” or as “Vaillantii
group”, particularly because they differ from the Cellar fungus and Dry rot
fungus by their mycelia, strands, and fruit bodies. The polypores, particularly
A. vaillantii, form a well-developed white and cottony surface mycelium without
“inhibition colors”, which, thus, can be confused with the young mycelium
of the Dry rot fungus. Polypore mycelium spreads ice flower-like over the substrate,
that of the Dry rot fungus is converted with ageing into silvery-grey
skins, and that of the cellar fungi is dominated by fine black strands. White
(A. vaillantii), to string-thick, smooth and flexible strands develop within
the mycelium and grow over non-woody substrates and also through porous
masonry (Grosser 1985), the latter, however, less intensive than by the Dry
rot fungus. The white to yellow (A. xantha) orred(O. placenta f. placenta)
fruit bodies show pores that are visible with the naked eye (Fig. 8.19). The
dry wood shows the typical brown-cubical rot. It is often said that the cubes
caused by the polypores and the cellar fungi are smaller than those by the
Dry rot fungus. The cube size varies however also as a function of the wood
moisture content (Grosser et al. 2003). After advanced decay, the dried substrate
of most brown-rot fungi can be ground with the fingers to a brown
powder (“lignin”).
The polypores attack predominantly coniferous woods in damp new and
old buildings, particularly in the upper floor, furthermore mine timber, stored
timber as well as timber in outside use, particularly in the soil/air zone, such
as poles and sleepers. They also attack trees as wound parasites and live
on stumps and fallen trees (Krieglsteiner 2000). Antrodia serialis was found
in over-mature Sitka spruce trees (Seehann 1984). “Dry” wood should not
become infected. In the laboratory, however, wood of 22% moisture content
was colonized (Table 8.7). As so-called “wet-rot fungi” (Coggins 1980; Bravery
et al. 2003), they need wet wood with moisture contents from 30 to 90% u for
a long time. According to literature, the optimum is around 45% (Table 3.6).
Laboratory experiments revealed that minimum moisture for wood decay by
A. vaillantii was 29% and the optimum 52 to 150% (Table 8.7). With timber
drying, Antrodia species were supposed to die (Bavendamm 1952c; Coggins
1980). However, more convincing seems that they only stop growth (Grosser
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